1. Field
Embodiments relate generally to alkali-free glasses and more particularly to alkali-free, high strain point and/or intermediate expansion coefficient, fusion formable aluminosilicate, and/or boroaluminosilicate glasses which may be useful in photovoltaic applications, for example, thin film photovoltaic devices.
2. Technical Background
Substrate glasses for copper indium gallium diselenide (CIGS) photovoltaic modules typically contain Na2O, as diffusion of Na from the glass into the CIGS layer has been shown to result in significant improvement in module efficiency. However, due to the difficulty in controlling the amount of diffusing Na during the CIGS deposition/crystallization process, some manufacturers of these devices prefer to deposit a layer of a suitable Na compound, e.g. NaF, prior to CIGS deposition, in which case any alkali present in the substrate glass needs to be contained through the use of a barrier layer. Moreover, in the case of cadmium telluride (CdTe) photovoltaic modules, any Na contamination of the CdTe layer is deleterious to module efficiency and, therefore, typical Na-containing substrate glasses, e.g. soda-lime glass, require the presence of a barrier layer. Consequently, use of an alkali-free substrate glass for either CIGS, silicon, wafered crystalline silicon, or CdTe modules can obviate the need for a barrier layer.